1. Field of the Invention
The present invention relates to a power supplying circuit which supplies the supply voltage from a power source circuit to a load apparatus. The power supplying circuit of the present invention is suitable for use, for example, in power supply to an external accessory of a video tape recorder incorporating a camera and in driving of a battery charger and a motor.
2. Description of the Prior Art
Conventionally, in supplying the supply voltage from a power source circuit to a load apparatus, a protecting circuit part such as a fuse (an integrated circuit (IC) protector when the load apparatus is an IC) is provided between the power source circuit and the load apparatus. When the power supply is abnormal, the power supply to the load apparatus is stopped by breaking the protecting circuit part such as a fuse and an IC protector.
For example, when the supply voltage is supplied from a power source circuit of a video tape recorder incorporating a camera to a zoom microphone which is an external accessory of the video tape recorder, if the amount of current flowing to the zoom microphone increases due to a disorder such as a short circuit, a fuse provided in the video tape recorder incorporating a camera breaks to stop the power supply.
However, in the conventional power supplying circuit of such an arrangement, since the protecting circuit part such as a fuse and an IC protector breaks when the power supply is abnormal, once the power supply is stopped by the working of the protecting circuit part, the power supplying state can be restored without the protecting circuit part being replaced. Thus, it requires a long time to resume the power supply.
To solve this problem, an arrangement as shown in FIG. 4 is considered in which a means 11 is provided for monitoring the voltage supplied to a load apparatus 12, and when the supply voltage becomes a predetermined value or lower, a switch means 10 inserted in a power supplying circuit 13 is broken to stop the power supply. To resume the power supply, the switch means 10 is reset by a manually operated resetting means 14.
However, according to this method, since the stop of the power supply is executed based on the drop of the supply voltage, the power supply is stopped even by an instantaneous rush current, and the power is not supplied until the switch means 10 is reset. For example, in the case of the video tape recorder incorporating a camera, an accessory is attachable to its body and the accessory has a supply terminal for receiving power so that power is supplied from the video tape recorder to the accessory. When the accessory is connected some time after the video tape recorder is turned on, a rush current i is generated to charge a decoupling capacitor (electrolytic capacitor) 9 of the accessory to break the switch means 10. Then, no power is supplied to the accessory until the resetting means 14 is operated.